This invention relates to a digital video effect system responsive to a plurality of nonsynchronous or individually synchronized input television signals for producing a combined or mixed television signal phase-locked to a reference timing signal. The mixed television signal represents a picture composed of predetermined areas of the respective pictures represented by the input television signals.
As will be described later with reference to a few of several figures of the accompanying drawing, a conventional digital video effect system comprises a plurality of converters for converting the input television signals to corresponding sequences of digital video signals and a plurality of large-capacity memories, such as one-frame memories, for the respective input television signals. It is possible to reduce the total memory capacity to about a half by using the memory disclosed in connection with a phase locking system in U.S. Pat. No. 4,007,486 issued to Masao Inaba et al, assignors to the instant assignee, of whom Kazuo Kashigi is one of the present joint inventors. Use of the memories of the type taught in the referenced United States patent is, however, inconvenient in some applications of the digital video effect system.
The above-mentioned predetermined area of a picture represented by a particular at least one of the input television signals is often varied in size on composing the picture represented by the mixed television signal. Compression of the picture size is achieved by using the memory for the particular signal also in thinning out the digital video signals derived therefrom. Mere thinning out, however, means a loss of the information given by the particular signal. As a result, the composed picture is adversely affected both in continuity and linearity.